Manufacture of rubber



Patented Apr. 6, 1943 UNlTED STATES PATENT OFFICE No Drawing.Application April 24, 1940, Serial No. 331,384

8 Claims.

This invention relates to improvements in the technique of processinghigh carbon black-rubbermixes prior to vulcanization thereof.

The technique of processing high carbon blackrubber mixes prior tovulcanization thereof, whereby to obtain vulcanizates with improvementsin physical and chemical properties, is described in Gerke et al. U. S.P. 2,118,601. The improved vulcanizates prepared by this techniquediffer from the usual vulcanizates produced by older techniques in thatthey have relatively (1) lower modulus at low elongation, (2) highresistance to abrasion, (3) higher modulus above 300% elongation, (4)low torsional hysteresis, (5) high electrical resistivity, and are (6)relatively softer.

These aforesaid vulcanizates are obtained by incorporating in the rubbera relatively large amount of carbon black, for example, at least 25parts, and preferably at least 40 parts in the case of the tiretreads,by weight of carbon black per 100 parts by weight of rubber, andthen subjecting a substantially homogeneous mixture of the ingredientsto a heat treatment at a temperature substantially above 250 F., thepreferred temperatures being in the range from about 300 F. to 370 F.,and masticating the mix during and/or after such heat treatment, oralternately therewith. The duration of the special heat treatment mayvary with the temperature employed, the higher the temperature theshorter the time, and is governed also by the degree of change desiredin the properties of the ultimate vulcanized product which propertiesare gauged to be compatible with its final use. In general, heattreatments of from 10 to 60 minutes duration will be found suitable formost purposes, and particularly within the preferred temperature range.

An object of the present invention is to get the desired effects of heattreatment in a shorter period of time, and to provide an agent orpromoter to speed up the process of attaimnent of the desired propertiesduring the technique of processing described in U. S. 2,118,601. I havediscovered that the heating operation can be materially shortened byadding to the mixture of rubber and carbon black, prior to the heattreatment a class of chemicals capable of facilitating the said process,viz., organic di(primary) amines. Examples of such chemicals arep,p'-diaminodiphenyl methane, benzidine (p,p'-diaminodiphenyl),polyethylene polyamine (product of reaction ammonia with ethylenedichloride; boil-- ing range ZOO-375 C.), ethylene diamine, diethylenetriamlne, triethylene tetramine, rename, p-

phenylene diamine, naphthalene diamine-1,4; 0- methyl p-phenylenediafnine; p,p-diamino benzhydrol; p, p di ami'nO diphenyl ketone;p,p'-diaamino triphenyl methane; pgppf tria'rnino triph'enylmethane;p,p'-diamino' diphenyl ethane; p,p-diamino diphenyl piper'azine;p,p-diamino diphenyl ethylene 'diamine, p,p"-diamin'o' diphenyl ether,etc. Also included in the scope of the invention are the simplesubstitution products of the above as alkyl, aryl, alk'oxy, halogen, andnitro substituted bodies. Of the aromatic substances, those having a;para di-amine structure are preferred. v The promoter increases the rateof increase of electrical resistivity in the process of U. S. P.2,118,601.

The invention is further specifically illustrated with respect to theprocessingof tire tread compositions, it being understood that suchcompositions before they are vulcanized are to be subjected to the usualsteps of shaping, manipulation and mounting attendant upon'the manufacture of a vehicle tire, whether of the solid or pneumatic variety, andin which the final article embodies at least as its tread portion, theVulcan ized composition of the invention.

In the following examples illustrating the invention, the parts are byweight and refer to parts per parts of rubber.

Example 1 A master batch consisting of 100 parts of smoked sheet rubber,55 parts of carbon black and 2 parts of pine tar was mixed on a millwith the mill roll temperature at about F. for about 20 minutes untilthe carbon black was thoroughly incorporated. Higher mill temperaturesmay be used even up to 260 F. which is sometimes reached at the end of aten minute Banbury cycle in factory master batching. This master batchwas divided into two portions and, to one portion A, 0.2 part ofp-,p'-diaminodiphenyl methane was added on a cool mill and the millingcontinued until the chemical was thoroughly and substantiallyhomogeneously incorporated. Also the other portion B which is thecontrol containing no added chemical was milled for the same length oftime.

Both mixes A and B were then milled 10 min utes at 300 F. After coolingat least five minutes these were recovered; i-. e. reduced to aviscosity suitable for milling in of further compounding ingredients, ona cool mill and the following ingredients were added by conventionalmixing: 2.5 parts of zinc salt of cocoan'ut' oil acids, 2.0 parts ofKatie brand zinc' oxide,'0.9

part of methylene aniline-butaldehyde acceler.

ator, 2.0 parts of acetcne-diphenlamine reaction product (antioxidant)and 4 parts of sulfur. The stocks were vulcanized 60 and 90 minutes at45 pounds steam pressure and the vulcanized stocks showed the followingproperties:

The above data show definitely that the presence ofp,p'-diaminodiphenylmethane in stock A has speeded up the obtaining ofthe benefits of the heat treatment process.

Example 2 A master batch consisting of 100 parts of smoked sheet rubber,and 50 parts of carbon black was mixed in a conventional manner as setforth in Example 1 whereby the carbon black and rubber are thoroughlyand substantially homogeneously mixed. This master batch was dividedinto two portions and, to one portion A, was added 0.2 part of benzidinein a conventional manner whereby the chemical is thoroughly andsubstantially homogeneously incorporated. The other portion B,containing no chemical, was given the same amount of milling.

Both mixes A and B were then milled minutes at 300 F. After cooling atleast five min- Cure A B Tensile and per cent elonga- {60 mins... 3710450 3965 520 tion at break. 90 mini 3856 420 4141 520 Abrasion and Adamshard- {60 mins.-- M2 33 133 35 ness. 90 mins 145 31 136 28 Example 4 Amaster batch consisting of 90 parts of smoked sheet rubber, 50 parts ofcarbon black, 4.5 parts of stearic acid, and 1.6 parts of pine tar wasmade by mixing on a mill at not over 180 F. (rubber temperature). Theresulting master batch was divided into two portions and to one portionA was added 0.25 part of p,p-diaminodiphenylmethane on the mill at notover 180 F. (rubber temperature). The other portion B containing nochemical was given the same amount of milling at the same temperature asA.

Both mixes A and B were then divided in portions and heated in steam at65 pounds pressure for 30, 60 and 120 minutes. After cooling at least 5minutes, these mixes were recovered on a cool mill and the followingingredients were added on a mill at not over 180 F. rubber temperature;

utes, these mixes were recovered on a cool mill 35 10 parts of smokedsheets, 0.4 part of pine tar, and the following ingredients were addedby con- 2 parts of Kadox brand of zinc oxide, 1.25 parts ventionalmixing; 3 parts of zinc salt of cocoanut of acetonediphenylaminereaction product, 0.35 oil acids, 2.0 parts of Kadox zinc oxide, 3.5parts part of diphenyl-p-phenylene diamine, 1.125 of sulfur, 1 part ofpalm oil, 5 parts of pine tar, parts of methylene orthotoluidine-mercaptoben- 0.9 :part of the reaction product of methyleneanizothiazole reaction product and 2.625 parts of sulline andbutyraldehyde, and 1 part of acetonefur. The stocks were then vulcanized35 and 70 diphenylamine reaction product. The stocks minutes at 50 lbs.per sq. in. steam pressure and were Vulcanized 60 and 90 u es at poundsshowed the following properties:

i A B 3800 585 ssoo 500 3000 565 3000 505 81151165 and Per cent ehngamnat break" 3500 590 3100 525 3100 520 3500 s95 i Tor ion hysteresis 13% jj El ctrical resistivity (Log R) 3 3:: g}; g 3.2

104 37 171 30 1'3 as 8 4 Abram and Adamshnrdncss 187 40 133 42 1c? 41 i74 37 steam pressure and the vulcanized stocks showed 55 Emample 5 thefollowing propertlesi An example showing the effect of various Cum A Btimes of milling is as follows:

A master batch was made consisting of 100 parts of rubber 55 parts ofcarbon black and 1 00 4000 540 4121 ii g fa n ifigaifi {m in 357; 5403770 040 60 3.5 parts of pine tar. To a portion A of this 1x1 011 andAdams $33: L32 3; master batch on a mill at 140 F. was incorporated 0.25part of p,p-d1annno diphenylmethane Emmple 3 per 100 parts of rubber. Aportion B without A master batch consisting of 100 parts smoked 05 gf igi g was fi as controla sheet rubber, parts of carbon black and 2.5 1020 3 s en 1111 ed at 00 F. for parts of pine tar was made byconventional milla 0 After 2. or at ing as set forth in Example 1. Thismaster batch least 15 the es were recovered on was divided into twoportions, and to one a cool mill, and then the following ingredientstion A was added 0.2 part of polyethylene polye added! 5 p rts of Kadoxbrand of zin amine, by conventional milling. The other poroxide, 3.5parts of zinc soap of cocoanut oil tion B containing no chemical wasgiven the same acids, 3.0 parts of sulfur and 1.0 part of formamount ofconventional milling. aldehyde aniline-mercaptobenzothiazole reac- Bothmixes A and B were then milled 10 mintion product. I utes at 300 F.After cooling at least five min- These mixes were cured 60 minutes at 30pounds steam pressure and the finished stocks showed the followingproperties:

Time of A B milling of master gfi fi Cure-=60 min. at 30 lbs.

mi 4340 4300 Tensile Strength :53 {3331: itit i333 r 60 min '3860 405010 min- .103 1 44 Torsional hysteresis (at min .094 104 280 F.). min 080097 6 0'min .062 .073 10 min }0.5 ]8.0 Electrical resistivity (Log R) $360 min 12. l .2.1

10 min 140.0 61 178. 0 62 Grasselli abrasion and Shore 20 min. 134. 5 58144. 5 59 hardness. 30 min. 126. 5 59 139. 5 59 60 min. 113.5 58 119,558

The above data plainly show the eifect of the chemical on speeding upthe effect of attaining maximum properties.

Electrical resistivity was determined by measuring the resistance of aspecimen of known thickness (about 0.1 inch) placed between mercuryelectrodes, under a potential difference of 135 volts, using a sensitivegalvanoineter with an Ayrton shunt. In the tables of data herein,

the logarithm (to base 10) of the specific electrical resistivity(ohm-ems.) is 10g R,-

The torsional hysteresis represents the logarithmio decrement (base 10)of the observed designated amplitudes of successive oscillations of atorsion pendulum, measured at 280 F. (137.8 C.) with an apparatusconsisting essentially of a torsion pendulum in which the sample ofrubber tested supplies the restoring force when the pendulum isdeflected. For further description of this testing see U. S. P.2,118,601.

The abrasion resistance is expressed by figures which are inverselyproportional to the amount of wear (reduction in thickness) effectedduring a fixed number of cycles on the United States Rubber Companyabrasion testing machine. The machine is operated with the abrasivewheel rotating at 180 R. P. M. and with a total load on the sample ofsix pounds.

In the Grasselli abrasion test which is used in Example 5, the abrasionresistance is expressed in cubic centimeters of material removed perhorse power hour. This test is described in A. S. T. M. Standards onRubber Products for October, 1935, pages 42 to 44.

The visible changes taking place in the hot milling method as describedin the above examples are somewhat similar to those described in U. S.P. 2,118,601. However, the viscosity increase during high temperaturetreatment may even be greater. As the hot milling proceeds the mixfinally begins to smooth out. The

smoothing out need not necessarily be done on the hot mill but it may besubsequently carried out on a cool mill. In the steam process in whichthe mix is not milled during heating, smoothing out does not occur inthe heater but is obtained upon the relatively cooler recovery mill.

The invention is not limited in the amount of chemical, although thepreferred amounts vary from 0.05 to 2.0 parts per one hundred parts ofrubber.

The use of these chemicals is not limited to the purity of the chemical.The pure chemic'als or crude reaction product from the preparation =ofthese chemicals or admixtures of these chemicals with other chemicals orcompositions may be used to speed-up the heat treatment black, and thenthe-resulting master batch-subjected to the heat treatment. It isunderstood that this is controlled within limits avoiding seriousdegradation of the rubber since it is known that either excessivemilling of rubber in air or excessive heating at elevated temperaturesof rubber tendsto break down (degrade) the rubber molecules. Rubbervulcanizates made from degraded rubber have unusually low tensilestrength, poor resistance to tear, and poor resistance to ageing. By thepresent invention the tensile strength of the resulting vulcanizates isnot lowered more than 10% by the'heat-treatment. Instead of heattreating on a' mill, the heating may be conducted in a heater in anatmosphere of hot air, steam, nitrogen, or a mixture of air and steam,or in Water, etc. Where heating is carried out in a medium such as steamor a mixture of air and steam, the stock is preferably heated while inthin layers, while the mixture is static, i. e. there is no mechanicalagitation of the mixtaking place, as distinguished from a masticating ormilling operation. Also, in carrying out the invention the usualsofteners and other ingredients, may be included, if desired, in theinitial mixture of rubber, black and chemical for the purpose ofsoftening the rubber and facilitating the admixture and distribution ofthe black therein, or for the purpose of improving the properties of thefinal vulcanizate; for example, such softeners as oils, tars, fattyacids, fatty acid soaps, and mineral rubber, may be added. The rawrubber may also be blended with reclaimed rubber in any proportions. Therubber used in the master batches may have been softened by any of theprocesses known to the art, such as heating in air, steam or mixturesthereof, or mastication in the presence of zinc oxide, zinc soaps, leaddioxides, or other types of plasticizing agents.

Whereas the invention is adaptable broadly to all kinds of black it isparticularly concerned with what are known as rubber reinforcing blacks,which blacks are herein distinguishable from the so-called soft rubberblacks of larger particle size, which are non-reinforcing, andflocculable to a lesser extent by heat, and fro-m blacks of extremelysmall particle size like paint black and ink black.

While the invention is particularly significant in relation to tiretread compositions, it is also applicable to the manufacture of anyrubber products in which are desired the qualities of high abrasionresistance, toughness, flexibility, high electrical resistivity or lowhysteresis, etc., such as footwear outsoles, pneumatic inner tubes,hose, belting, vibration-absorbing mountings, tank linings, etc.

The term rubber is used in its usual generic sense applicable tocaoutchouc and similar vulcanizable gums, as well as to varioussynthetic rubbers and rubber-like products which have properties incommon with natural rubber whereby they may be adapted to the samecommercial uses.

The use of these compounds is not limited as to the temperature, time,pressure, or method of vulcanization. Also vulcanizing agents other thansulfur may be used for the vulcanization of; the compounds used, Theymay be used in rubber mixes subjected to mold cures, air cures, ammoniacures, submarine cures, steam cures, etc. r

The promoters, as stated above, may be added before or during heattreatment, may be putinto the rubber by mill incorporation, byimpregnation, or otherwise.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A process which comprises mixing rubber with a relatively largeamount of carbon black, and a small amount of a di(primary) amine,heating the mix to a temperature substantially above 250 F. to severelyfiocculate the black, and thereafter masticating the mix tosubstantially completely disperse the fiocculated black.

2. A process which comprises mixing rubber with a relatively largeamount of carbon black, and a small amount of an aliphatic di(primary)amine, heating the mix to a temperature substantially above 250 F. toseverely fiocculate the black, and thereafter masticating the mix tosubstantially completely disperse the flocculated black.

3. A process which comprises mixing rubber with a relatively largeamount of carbon black, and a small amount of an aromatic di(primary)amine, heating the mix to a temperature substantially above 250 F. toseverely flocculate the black, and thereafter masticating the mix tosubstantially completely disperse the fiocculated black.

4. A process which comprises mixing rubber with a relatively largeamount of carbon black, and a small amount of an aromatic para-di-(primary)amine, heating the mix to a temperaturesubstantially above 250F.,to severely flocculate the black, and thereafter masticating the mixto substantially completely disperse the flocculated black.

5. A process which comprises mixing rubber with a relatively largeamount of a rubber reinforcing black, and a small amount of adi(primary) amine, heating the mix to a temperature substantially above250 F., and thereafter masticating the mix and completing incorporationof additional compounding ingredients and vulcanizing ingredients.

6. A process which comprises mixing rubber with a relatively largeamount of a rubber reinforcing black, and a small amount of a p,p-diaminodiaryl methane, heating the mix to a temperature substantiallyabove 250 F., and thereafter masticating the mix and completingincorporation of additional compounding ingredients and vulcanizingingredients.

7. A process which comprises mixing rubber with a relatively largeamount of carbon black, and a small amount of a di(primary) amine,heating the mix to a temperature in the range from about 300 F. to about370 F., and thereafter masticating the mix and completing incorporationof additional compounding and vulcanizing ingredients.

8. A process which comprises mixing rubber with a relatively large amount of carbon black, and a small amount of a di(primary) amine,heating the mix to a temperature substantially above 250 F. and notabove about 370 F. to severely flocculate the black, and thereaftermasticating the mix for a time sufiicient to substantially completelydisperse the flocculated black.

' LOUIS H. HOWLAND.

